The thing about using the set is that you can use rapid fire every 8s. Without the set equipped the same torp fires only once every 15 s, so it makes a massive difference. Unless my set was bugged....
transphasic torps normally have a 10sec cooldown, the rapid fire have an 8sec cooldown. they hit as hard as normal transpasics BUT they only have the acc and i think crit hit bonus (plus the time reduction) making them very rare (which also means they get the +15% damage bonus over common ones)
in my luna i use them, theyre great. i run the delfector and the shield to get the extra damage boost and power transfer, i also run a regular eps and use rapid fire with 2 turrets and a cannon..
the set isnt for everyone for sure, but its neat to have.